The present invention relates to circuits used in electronic packages. In particular, the invention relates to methods for preparing circuit elements that when bonded to other circuit elements form circuits with improved electrical and mechanical connections between adjacent circuit elements. The present invention additionally relates to circuits formed from the circuit elements prepared by the methods of the present invention.
Contemporary electronic devices require multiple circuit elements including, for example, integrated circuits, flexible circuits, single and multi-layer circuit boards, chip scale packages and ball grid array packages. These circuit elements must be connected by multiple precise mechanical and electrical connections in order for the devices to function reliably. Numerous approaches have been made to make reliable electrical connections in a low cost and efficient manner. These approaches have met with varying degrees of success.
One basic approach involves plated through hole (PTH) printed wiring board fabrication processes, for making the mechanical and electrical connections in separate processing steps. A typical mechanical connection between printed circuit boards is made by placing a sheet of adhesive resin impregnated fiber mat between two double sided printed circuit boards to form an assembly. This assembly is then placed in a lamination press and bonded under heat and pressure, mechanically connecting the boards.
Electrical connection then occurs in a separate series of steps, commonly known as a plated through hole (PTH) process. This PTH process typically includes drilling holes in the circuit board where electrical contact between layers is desired, to create a via. These vias include walls that are cleaned and plated with conductive metallurgy.
However, this conventional PTH fabrication has several drawbacks. There are yield losses and reliability issues associated with the multiple step processing in PTH technology, resulting in increased costs as circuit feature size is reduced.
Processes that form the mechanical and electrical connections simultaneously potentially simplify the manufacturing process and reduce costs associated therewith. One method of simultaneously forming mechanical and electrical connections employs an adhesive ply with conductive buttons to attach circuit elements. For example, U.S. Pat. No. 5,282,312 (DiStefano et al.) discloses two metal flexible circuits patterned with PTH vias. The connection between circuit layers is made by an adhesive bond ply with patterned conductive buttons. The buttons are placed in the bond ply at locations where connections are desired between the circuit layers. The adhesive bond ply has sufficient rigidity such that conduction through the bond ply is only permitted at conductive buttons. One drawback to this construction is the required complex patterning process and subsequent registration of the bond ply to the circuit layers, that adds cost and decreases yield.
Another approach to making circuit element connections, such as those between chips and boards, flexible circuits to boards and other related circuit structures, and also to form inter-layer connections in circuit boards, involves making the mechanical and electrical connections simultaneously in one press step or a series of steps. An example of this approach involves using anisotropic or z-axis adhesives, a recently developed class of conductive adhesives, to replace solder for surface mounting. These anisotropic adhesives include adhesive films loaded with conductive particles at a much lower volume fraction than conventional isotropically conductive adhesives.
In operation, when pressed between conductors of circuit elements, the anisotropic adhesive film is compressed, such that the adhesive is forced out of the way of the conductors, while the conductive particles remain trapped between the conductors, formning electrical contacts therebetween. It is important for these anisotropic adhesive films to have a conductive particle loading that is sufficiently disperse to prevent particle shorting in the plane of the circuit.
U.S. Pat. No. 5,502,889 (Casson et al.) discloses a method for fabricating a multilayer circuit board, that uses an anisotropically conducting adhesive to connect multiple layers of double sided circuitry. However, the resultant circuit has drawbacks, in that the use of a random dispersion of particles can not provide the high density of hole (or via) interconnections required for high performance circuits due to the possible electrical shorting between contacts. In addition, the random dispersion of particles requires patterned masking of the circuit layers to prevent shorting between layers.
Circuit elements have also been connected with nonconducting adhesives, by using patterned bumps on the circuit elements. For example, U.S. Pat. No. 4,749,120 (Hatada) describes a mechanical connection between a semiconductor device having an array of conducting bumps and corresponding pads on a wiring board, with a nonconducting adhesive. During the bonding process, the bumps are forced through the adhesive, making electrical contact with their respective pads.
U.S. Pat. No. 5,401,913 (Gerber et al.) discloses multiple circuit layers having columns (bumps) of a metal. The circuit layers are mechanically connected by a nonconducting adhesive layer placed between each successive circuit layer. The circuit layers are subsequently laminated in the presence of heat and pressure, such that the bumps are forced through the adhesive layer and contact their respective pads on the adjacent circuit layer.
For many of the above described interconnection techniques, it is requisite that the respective conducting particles or bumps penetrate the adhesive layer, in order to form an electrical connection between conductive members of the circuit elements. This requirement puts significant constraints on the selection of adhesives. For example, insufficient flow can result in trapping small amounts of adhesive between the conducting elements, resulting in high resistance bonds and/or environmentally unstable bonds. Alternately, too much flow of the adhesive typically results in adhesive deposits in undesired locations on the circuit elements or resultant circuit as well as bond line nonuniformity, detrimental to electrical performance. Excess adhesive flow can also starve regions in the bond of adhesive, resulting in voiding or regions of very thin bond lines, leading to reduced adhesion and poor environmental performance.
To accomplish the above objects, the invention provides a connector system comprising a pair of first and second connectors, each of which includes a fitting portion to be fitted with a counterpart fitting portion in a mutually inserting manner to establish an electrical connection between the first and second connectors, and a polarizing key mechanism permitting only a specific combination of the first and second connectors to be connected with each other, characterized in that the polarizing key mechanism comprises a first guide member provided around the fitting portion of the first connector, the first guide member including a plurality of engaging sections; and a second guide member provided around the fitting portion of the second connector, the second guide member including a plurality of engaging sections which can be compensatingly engaged with the plurality of engaging sections of the first guide member; wherein the first and second guide members permit the first and second connectors to be connected with each other only when the engaging sections of the first guide member are compensatingly engaged with the engaging sections of the second guide member, and guide the first and second connectors under a compensating engagement between the engaging sections in such a direction as to cause a parallel translation of the fitting portions of the first and second connectors while maintaining a face-to-face arrangement of the fitting portions.
The invention further provides a connector system as set forth above, wherein the engaging sections of each of the first and second guide members are located at both sides of a horizontal sectional center plane dividing the fitting portion of each of the first and second connectors into upper and lower parts and at both sides of a vertical sectional center plane dividing the fitting portion into right and left parts.
The invention further provides a connector system as set forth above, wherein the fitting portion of each of the first and second connectors has a polarity, and wherein the engaging sections of each of the first and second guide members are located at positions symmetric with respect to a center point of the fitting portion of each of the first and second connectors.
The invention still further provides a connector system as set forth above, wherein the polarizing key mechanism further comprises a first abutting section provided in the first connector in association with the first guide member for abutment with another connector which cannot be compensatingly engaged with the first guide member to prevent the first connector from being connected with the other connector, and a second abutting section provided in the second connector in association with the second guide member for abutment with further connector which cannot be compensatingly engaged with the second guide member to prevent the second connector from being connected with the further connector.
The invention still further provides a connector system as set forth above, wherein the first guide member includes a first wall substantially surrounding the fitting portion of the first connector, the engaging sections of the first guide member being grooves formed on the first wall and extending along a direction of insertion of the first connector to the second connector, and wherein the second guide member includes a second wall substantially surrounding the fitting portion of the second connector to define a gap for receiving the first wall between the second wall and the fitting portion, the engaging sections of the second guide member being ribs formed on the second wall and extending along a direction of insertion of the second connector to the first connector, the ribs being adapted to be compensatingly engaged with the grooves.
The invention still further provides a connector system as set forth above, wherein the first connector includes an insulation body provided with the fitting portion and supporting a plurality of contacts, and a shell for covering the insulation body, and wherein the first guide member is structured as a frame member attached to the shell.
The invention still further provides a connector system as set forth above, wherein the first connector includes an insulation body provided with the fitting portion and supporting a plurality of contacts, and a shell for covering the insulation body, and wherein the first guide member is structured as a part of the shell located around the fitting portion.
The invention still further provides a connector system as set forth above, wherein the second connector includes an insulation body provided with the fitting portion and supporting a plurality of contacts, the insulating body being secured to a panel with an opening into which the fitting portion is inserted, and wherein the second guide member is structured as a frame member attached to the panel.
The invention still further provides a connector system as set forth above, wherein the second connector includes an insulation body provided with the fitting portion and supporting a plurality of contacts, the insulating body being secured to a panel with an opening into which the fitting portion is inserted, and wherein the second guide member is structured as a frame part integrally formed with the panel.